set blob not share mem by default (#1133)

oneflow/core/job/job_conf.proto

@@ -61,7 +61,7 @@ message OtherConf {
   optional bool use_ordered_allreduce_in_mdupdt = 115 [default = false];
   optional bool use_synthetic_data =  116 [default = false];
   optional bool enable_write_snapshot = 130 [default = true];
-  optional bool enable_blob_mem_sharing = 140 [default = true];
+  optional bool enable_blob_mem_sharing = 140 [default = false];
 
   oneof JobType {
     TrainConf train_conf = 200;